The present invention relates to drill bits for percussive rock drilling tools and, more particularly, to such drill bits that use hard buttons.
A known percussive drill bit with a plurality of inserts is disclosed in US 2008/087473. Further, another down-the-hole percussive hammer is disclosed in WO 02/40820.
In rock drilling applications devices such as down-the-hole hammer devices or rock drills that have drill bits with a plurality of buttons mounted thereon are often used. The buttons can be made of a material such as cemented carbide that is harder than the material from which the body of the drill bit is made. At the forward end of the drill bit, the front surface of the drill bit head on which the buttons are mounted is ordinarily formed to have a central area that shall be denominated for purposes of the present discussion as a face surface and a surrounding, frustoconical area that is typically referred to as a gauge or a gauge surface. One or more flow openings ordinarily extends through the length of the drill bit and leads to a flow channel formed in the front surface of the drill bit head. Flushing fluid is introduced to the drilling site through a drill tube attached to the drill bit and debris is flushed from the drilling site via axially extending grooves formed along the sides of the drill bit head. Gauge buttons fixed to the gauge wear heavily since they are subjected to more load than other buttons. The life of such heavily wearing gauge buttons constitutes the effective life of the bit.
The provision of a substantial number of buttons on the gauge can facilitate the drilling process, such as by providing good protection for the peripheral edges and grooves of the drill bit head and thereby maintaining satisfactory flushing of debris.
Moreover, in the area of the axially extending grooves, there is often insufficient space along the gauge to provide a hole for a button and consequently, buttons on the gauge can be more subject to excessive. Therefore it desirable to provide a drill bit that has a relatively high wear volume around its periphery and to provide a drill bit that permits more buttons to be disposed closer to the periphery of the drill bit.
According to an aspect of the present invention, a drill bit for rock drilling tools is provided and comprises a drill bit head having a front surface having a face surface defining a forward-most end of the drill bit head, at least one hole in the drill bit head for receiving a button, and at least one recess in the face surface, the recess being larger than the hole, and the hole being disposed in the recess so that an open end of the hole is disposed below the face surface.
A drilling tool comprising such a drill bit is also provided.